1. Field of the Invention
The present invention generally relates to methods and devices for monitoring a low concentration additive in a flowing treatment stream. In an embodiment, the present invention relates to methods and devices for monitoring the concentration of ferrate in a flowing treatment stream.
2. Description of the Related Art
Ferrate is a strong oxidant that can react with a variety of inorganic or organic reducing agents and substrates (R. L. Bartzatt, J. Carr, Trans. Met. Chem., Vol. 11 (11), pp. 414-416 (1986); T. J. Audette, J. Quail, and P. Smith, J. Tetr. Lett., Vol. 2, pp. 279-282 (1971); D. Darling, V. Kumari, and J. BeMiller, J. Tetr. Lett., Vol. 40, p. 4143 (1972); and R. K. Murmann and H. J. Goff, J. Am. Chem. Soc., Vol. 93, p. 6058-6065 (1971)). Ferrate can act as a selective oxidant for synthetic organic studies and is capable of oxidizing/removing a variety of organic and inorganic compounds from, and of destroying many contaminants in, aqueous and non-aqueous media.
Ferrate is of particular interest to water treatment because it provides a suitable mechanism for self-removal of ferrate from solution. In all oxidation reactions, the final iron product is the non-toxic ferric ion which forms hydroxide oligomers. Eventually flocculation and settling occur which remove suspended particulate matter.
The use of ferrate may therefore provide a safe, convenient, versatile and cost effective alternative to current approaches for water, wastewater, and sludge treatment. In this regard, ferrate is an environmentally friendly oxidant that represents a viable substitute for other oxidants, particularly chromate and chlorine, which are of environmental concern. Ferric oxide, typically known as rust, is the iron product of ferrate reduction. Therefore, ferrate has the distinction of being an “environmentally safe” oxidant. Although the oxidation reactions with ferrate appear similar to those known for MnO4− and CrO42−, ferrate exhibits greater functional group selectivity with higher rate of reactivity in its oxidations and generally reacts to produce a cleaner reaction products.
Previously, using ferrate in water treatment was problematic because of its lack of stability. However, recent discoveries have indicated that ferrate could be used at a site proximal to its generation, avoiding the lack of stability problem and opening up new applications. For example, U.S. Pat. No. 6,790,429, issued Sep. 14, 2004 and entitled “Methods of Synthesizing an Oxidant and Applications Thereof,” the entirety of which is hereby incorporated by reference, describes methods of continuously synthesizing ferrate in a reaction chamber and delivering at least a portion of the ferrate to a site of use that is proximal to the reaction chamber. U.S. Pat. No. 6,974,562, issued Dec. 13, 2005 and entitled “Methods of Synthesizing an Oxidant and Applications Thereof,” the entirety of which is hereby incorporated by reference, describes devices for continuously synthesizing ferrate for delivery to a site of use, wherein the site of use is at a distance from the output opening at which the concentration of ferrate at the site of use is equal to or greater than half the concentration of ferrate at the output opening. U.S. Pat. No. 7,476,324, issued Jan. 13, 2009, and entitled “Methods of Synthesizing a Ferrate Oxidant and its Use in Ballast Water,” the entirety of which is hereby incorporated by reference, describes methods of treating ballast water and methods of synthesizing ferrate at a site where ballast water is held. It is desirable to provide devices and methods that concern the use of ferrate and other low concentration additives in water and other treatments.